This invention relates to a power supply circuit comprising an input terminal, an output terminal and a reference terminal. A direct voltage source is connected to the input terminal and the reference terminal and a load is connected to the output terminal and the reference terminal. A series arrangement of an inductive element and a diode are connected to one another at a first node, the inductive element being connected between the input terminal and the first node and the diode being connected between the first node and the output terminal. A first electronic switch has a main current path connected between the first node and the reference terminal and a drive circuit periodically makes the main current path of the first electronic switch conductive and non-conductive.
The invention also relates to an electrical apparatus comprising such a power supply circuit.
Such a power supply circuit is known from U.S. Pat. No. 4,970,451. The known power supply circuit is of a configuration referred to in the literature as a "boost converter". Across the load an output voltage can be generated which is higher than the voltage from the direct voltage source. Converters of this type are used inter alia, in battery-powered apparatuses in order to boost the comparatively low battery voltage to the operating voltage of the electronic circuitry of the apparatus. The aim is then to enable operation with a minimal number of batteries in series and hence with a battery voltage which is as low as possible. Many battery-powered apparatuses have a so-called standby mode, which is necessary in order to prevent certain measurement data from being lost. For example microprocessors, random access memories and the like are thus maintained at a minimum operating voltage which is high enough to preclude the loss of information.